Jefferson County, IL Insulation Payback
Jefferson County, IL: what topping up your attic actually costs
DOE classifies Jefferson County as climate zone 4, mixed-humid — heating load in winter and cooling load in summer, both worth taking seriously here. Its recommended attic R-value for bare joists is R-60. Topping up a typical 1,000-square-foot attic from bare joists (R-2) to R-60 runs an estimated $3,480, and saves about $1,528 a year in heating and cooling — a payback around 2.3 years. That's about as fast as attic paybacks get.
The breakdown behind the number
The estimated savings split roughly $1,336/year heating, $191/year cooling. Out of every 100 US counties tracked here, Jefferson County's savings potential beats roughly 55 of them. Within zone 4 specifically, it ranks 135th of 825 counties by estimated savings. Illinois averages $1,642/year across the counties tracked here; Jefferson County comes in 7% lower.
Jefferson County's actual weather, not a national average
Jefferson County's climate figures — 4,998 heating and 1,191 cooling degree days a year — are read from MT VERNON 3 NE, IL US, 5.1 miles away, NOAA's nearest 1991-2020 normals station. Combined heating and cooling load puts Jefferson County in the 56th percentile of this 3,162-county dataset. Jefferson County falls in DOE's moisture regime A (humid), a detail that affects vapor-barrier recommendations more than the R-value target itself.
The smaller top-up scenario
A shallower starting point changes the math: with R-11 already down, only the gap to R-49 needs filling, at roughly $2,280 for an estimated $223/year saved (~10.2-year payback). This one is a genuine toss-up, not a clear yes.
Quotes and materials for this job
Actual quotes will vary by attic access, existing debris, and whether the job needs air sealing first. Treat the $3,480 figure above as a planning number for Jefferson County, not a bid - contractors typically charge a $600 minimum regardless of job size.
Nothing here is a guess
Every figure on this page traces to DOE/IECC climate zones and NOAA degree-day normals, documented in the methodology guide. The guide to what R-value actually means explains why R-60 is the target here specifically.